Why does alcohol increase aggression?

The intentionality bias is the tendency for people to view the behavior of others as intentional. This study tests the hypothesis that alcohol magnifies the intentionality bias by disrupting effortful cognitive abilities. Using a 2 x 2 balanced placebo design in a natural field experiment disguised as a food-tasting session, participants received either a high dose of alcohol (target BAC = .10%) or no alcohol, with half of each group believing they had or had not consumed alcohol. Participants then read a series of sentences describing simple actions (e.g., “She cut him off in traffic”) and indicated whether the actions were done intentionally or accidentally. As expected, intoxicated people interpreted more acts as intentional than did sober people. This finding helps explain why alcohol increases aggression. For example, intoxicated people may interpret a harmless bump in a crowded bar as a provocation.

Source: ““There Is No Such Thing as an Accident,” Especially When People Are Drunk” from Personality and Social Psychology Bulletin